METHOD AND DEVICE FOR UNPLUGGING A MOLTEN METAL DISCHARGE PORT

Abstract: Method and device for opening the outlet of a molten metal handling vessel, comprising a valve (6) having relatively moveable valve parts (7, 9 and 8, 11) and a frangible tube (13) through which gas can be passed, the tube (13) extending through the valve parts (7, 9 and 8, 11) into the outlet (5a) of the vessel, whereby opening the valve (6) by relative movement of the valve parts (9, 11) breaks the tube so that it does not obstruct opening, the end of the tube (13) having a cup-shaped seating portion (13a) to mate with a similarly-shaped recess in or adjacent the valve (6).

Description: Method and device for unplugging a molten metal di scharge port. This invention relates to molten metal handling vessels and is particularly concerned to provide an improvement in the opening of the bottom of the vessel, e.g. a ladle. Under the tap channel of the vessel is positioned a valve which comprises movable valve parts with flow passages which, in the valve's closed position, are displaced from each other and in the valve's open position are essentially in line with each other so that the melt can flow from the vessel through the flow passages. Valves of this type and their peripheral equipment are called sliding gate systems and are available in several designs, including those where the valve parts trace rectilinear translatoral relative movements and those where the valve parts trace relative rotary movements. Examples of valves of this type are described in WO/87/07306 among others. The invention will be further described below with reference to a ladle. In the bottom of the ladle there is a tap hole which leads to the sliding gate valve system. To prevent the melt running down into the valve, solidifying and blocking the tap channel, the tap hole is usually filled with sand. In spite of this it is a critical moment during the steel manufacturing process when a tap valve on a ladle filled with molten steel is to be opened to let the steel flow down into an ingot mould or tundish. What occurs in a proportion of cases is that the steel does not run out when the valve is opened due to some form of blockage in it or in the connection with the tap hole. The absence of spontaneous flow of the molten metal when the valve is opened results in a series of economic, as well as work environmental, related problems. Normally, the melt flows from the ladle through a protective tube, which prevents air from coming into contact with the liquid steel. When blockage of the tap channel occurs this protective tube must be removed to allow access with oxygen burning equipment to remove the obstacle. A pipe lance connected to an oxygen-line is then fed manually up into the tap channel so that the blockage can be burned out. During this operation, molten steel and slag splashes around the tap hole and as the obstacle is removed the steel flows in a violent stream down into the tundish close to the operator. The risks with this operation are quite obvious. Apart from the costs of the oxygen lance and oxygen, this operation can incur increased consumption of the refractory material of which the tap channel is constructed. Furthermore, since it takes time to open the blocked ladle, this can result in the optimal casting speed from the tundish to the mould not being achieved, which, in its turn, can cause deteriorated steel quality. In the worst case the casting must be stopped with subsequent preparations for the start of a new cast and reheating of the steel in the ladle. It has been proposed to blow argon gas into the tap channel just before the sliding gate is opened, by which means the channel is pressurised so that the high temperature sintered sand shell or possibly the solidified steel, which covers the mouth of the tap hole, is removed. The argon gas in this proposal has been introduced at the lower part of the tap channel in the valve's closed position and thus, under great resistance, must force its way up through the whole pillar of sand to reach the upper part of the channel. During trials of this proposal the sand has been blown away and steel has run down into the tap channel and had time to solidify before the valve could be opened. Even problems with sealing have been significant. Thus, for many reasons, there is a need to improve spontaneous tapping in conjunction with the opening of the ladle valve and it is an object of this invention to provide such improvement. Thus, the invention is based on the utilisation of gas, preferably argon gas, with a means of introducing it relatively high up in the tap channel. During the procedure, according to the invention, a tube of relatively frangible material is introduced into the tap channel where the tube in the closed position of the valve extends through both parts of the valve. Thereafter, gas is blown through the tube, whereupon the valve is opened during which the tube is sheared off. The sheared off end of the tube follows the outflowing sand before a stream of molten steel then follows during tapping, Accordingly, in one aspect the invention provides an apparatus to open and close an outlet in a molten metal handling vessel which includes a valve communicating with the outlet and having relatively movable valve parts, the valve parts having openings which are displaced from one another to close the valve and, hence, the outlet and which are in communication with each other and with the outlet to open the outlet, whereby the molten metal can flow out of the vessel, characterised in that there is provided a frangible tube through which gas can be passed, the tube being of sufficient length to extend through both valve parts and into the outlet of the vessel, whereby gas can be passed into the outlet and then opening of the valve by relative movement of the valve parts breaks the tube so that it does not obstruct opening and in that the end of the tube has a cup-shaped seating portion to mate with a similarly-shaped recess in or adjacent the valve. In another aspect the invention provides a method of opening and closing an outlet in a molten metal handling vessel in which a valve is positioned to communicate with the outlet, the valve having relatively movable valve parts, the valve parts having openings which are displaced from one another to close the valve and, hence, the outlet and which are positioned in communication with each other and with the outlet to open the outlet, whereby molten metal can flow out of the vessel, characterised in that a frangible tube is inserted through the valve parts into the outlet while the valve is in the closed position, gas is injected into the outlet through the tube to remove any obstruction to the outlet and the valve is opened thereby shearing off the length of tube in the outlet and in that the end of the tube is provided with a cup-shaped seating portion to mate with a similarly-shaped recess in or adjacent the valve . The relatively frangible tube may, for example, extend through a section of the movable valve part to one side of the valve's opening, i.e. its flow passage, and up through the opening, i.e. passage, in the fixed valve part. The cup-shaped seating portion of the frangible tube may conveniently seat in a correspondingly-shaped recess in a connector which is attached to the underside of the lower valve part, i.e. the movable valve part in a sliding gate valve. The cup-shaped seating portion may be, for example, of substantially hemispherical or part hemispherical shape and will for convenience be hereafter described with reference to those embodiments. Nevertheless it will be appreciated that the invention is not limited to those specific shapes. The hemispherical seating portion of the tube end is preferably of larger diameter than the diameter of the tube itself. Thus the hemispherical seating portion forms a bulbous extension at one end of the tube with the pole of the hemisphere furthest from the tube. The passage or passages though the tube for the gas must of course either continue through the hemispherical portion or enter the tube above it, the former being preferred. It is not necessary that the end of the frangible tube, i.e. the lower end in use, be a complete hemisphere and, indeed, it may be preferable to shape the seating portion so that it has a frusto- hemispherical shape with a flat lower surface and this arrangement may be found advantageous in respect of the provision of the gas flow passages through the tube, as will be explained in more detail later. The invention is advantageous in providing a means of securement of the frangible tube that can cater for less than totally accurate alignment of the tube through the valve parts when it is attached. Thus, without the hemispherical seating, it is possible that the tube can be fixed slightly out of the required line and it can then be damaged in its installation or in the operation of the valve so that it cannot function as required at the critical time. The invention overcomes this problem in a neat and effective manner. Any misalignment from the required line is readily taken up and adjustable by virtue of the hemispherical mating seating arrangement. In a further aspect, therefore, the invention provides a frangible tube having at least one longitudinal passageway through which gas can pass, one end of the tube having a cup-shaped, e.g. substantially hemispherically-shaped, seating portion to mate with a correspondingly-shaped recess in or adjacent an outlet valve of a molten metal handling vessel. The frangible tube is preferably made of ceramic material which can withstand the temperature of molten steel and which breaks easily when the valve is opened. It may be provided with several, e.g. four, axially extending gas passageways throughout its length. The tube with its hemispherical projection may be, for example, moulded or machined from a larger diameter tube. The provision of several small diameter axial gas passageways is advantageous in that when the valve opens, the gas tube breaks and a lower piece of it remains fixed in the moveable valve plate. If then the sliding gate valve has to be closed during ongoing tapping, the remaining piece of tube will form a plug so that the remaining accessible outflow area is defined by the hole or holes in the tube. Hence several smaller holes, while allowing gas through freely will impede the melt from passing through by its solidifying and thereby blocking its own passage. It is not necessary that the whole of the length of the tube be of the frangible material provided that the portion passing through the valve will break when the valve is opened. The remainder, i.e. upper part, of the tube may be e.g. of metal. The metal tube can fit into a suitable recess in the top of the frangible tube or vice versa or there may be a tight push fit between the two. Suitable adhesives may be used to hold them together, if desired. In a preferred embodiment, the attachment means of the frangible tube to the valve may include a connection to provide further adjustment to cater for misalignment of the tube from the required vertical position. This connection comprises a "floating spindle" in which the cup-shaped seating recess in the connector can move sideways, i.e. normal to the desired vertical axis of the frangible tube to cater for such misalignment. Such a connection is described more fully below with reference to the drawings. The invention is further described by way of example only with reference to the accompanying drawings in which: Figure 1 shows a section of the bottom part of a ladle with a sliding gate system set up in accordance with the invention; Figures 2, 3 and 4 are similar sections showing subsequent stages when opening the valve; Figure 5 shows on a larger scale a perspective view of a suitable design for the gas tube; Figure 6 shows in even larger scale, a view in the direction of arrow A of Figure 5; and Figure 7 shows an enlarged view of the region A of Figure 1 In the drawings, 1 denotes the bottom of a ladle, 2 the brick lining of the ladle and 3 a hole in the bottom of the ladle. A well block 4 is placed in hole 3 and is lined with a ceramic tube 5, (which is called the inner nozzle) and which defines the tap channel 5a of the ladle. Fixed to the ladle bottom 1 is a sliding gate valve system 6 which comprises an upper housing 7 and a similar lower, movable housing part 8. The sliding gate system 6 is a unit which can be attached to and then separated from the ladle. It comprises an upper housing 7 containing a refractory valve plate 9 and having a flow passage opening 10 therethrough and a lower housing 8 containing a refractory valve plate 11 with an exit channel 12. The upper part of the sliding gate system 7 is arranged so that in the position shown in the figure it is immovable relative to the ladle, whereby the flow passage opening 10 is positioned coaxially under the opening defined by the inner nozzle 5, i.e. it is coaxial with the tap channel 5a. In Figure 1, where the sliding gate system is shown in the closed position, the lower movable valve part 8 is positioned to the left side so that the exit channel 12 in the valve plate 11 is offset to the side of the flow passage opening 10 in the valve plate 9 and the surface of the valve plated 11 lies across and closes the tap channel 5a. As the sliding gate system is described it corresponds to known similar systems. According to the invention a gas tube 13 runs through the lower housing 8 and the portion of the valve plate 11 that closes off the tap channel 5a. The upper end of the gas tube 13 extends into the upper part of the channel 5a and its lower end sits in a seating connection piece 14 which abuts against the underside of the lower housing. A source, not shown, of gas can be connected to the gas tube via connection 14. The gas tube 13 is of a relatively frangible, i.e. a relatively brittle, refractory material. The lower end 13a of gas tube 13 is of frusto-hemispherical shape and sits in a similarly shaped recess in connection 14. This shaped end of the gas tube is described further below with reference to Figures 5 and 6. In the ladle above the brick lining 2, the well block 4 and the inner nozzle 5 there is a melt (not shown) and as known the tap channel 5a defined by nozzle 5 is filled with a good measure of sand (not shown) which in the contact area with the melt sinters to a dome-like crust 15. When tapping from the ladle is to take place, gas is blown in, preferably argon gas, through the connection piece 14 to break up the obstruction in the tap channel, i.e. the sintered sand crust 15, which in Figure 2 is shown in the broken up state. Due to the gas tube extending a considerable way up into the tap channel 5a (approximately three quarters of the nozzle height, measured from the bottom, has been shown to give good results), gas pressure is introduced just below the obstruction which is to be removed. Furthermore, most of the sand will be left in the nozzle and consequently prevents the melt from pushing down the nozzle with the attendant risk of solidification and blocking of the tapping channel. Also, the remaining sand gives a downward back pressure resulting in a decreased risk of leakage. However, if desired, a suitable gasket (not shown) may be positioned at the bottom of opening 10 in plate 9, surrounding tube 13 and sealing between plate 9 and movable plate 11. The gasket should be of compressible, non-porous, temperature-resistant material, e.g. a ceramic fibre material with covering a mica layer. As the gas pressure system does not effect the drive unit (not shown) for the valve opening, such as a hydraulic piston and cylinder unit, the movable lower housing part 8 can be moved to the right as Figure 1 to open the nozzle hole unit. In this connection the gas tube 13 meets the inner nozzle 5 inner wall and is cut off against the latter's lower edge. This position is shown in Figure 3. In practice, however, the gas tube will break earlier due to its inserted part being fixed by the sand in the inner nozzle 5. It is possible that the inserted part of the gas tube 13 above valve plate 11 will, in the meantime, be pushed away to the position shown in Figure 3. Continued opening movements uncover the whole of the tapping channel so that the melt can flow through the inner nozzle 5, through the flow passage opening 10 and then lower valve plate exit channel 12. Here the sheared off part of the gas tube 13 follows along. The remaining part of the gas tube 13 in the lower housing part 8 can, after completed tapping, be removed by releasing the (not shown) agent, which holds the connection piece 14 against the lower housing part 8. The frangible tube 13 is shown in greater detail in Figures 5 and 6. Its lower end has a frusto-hemispherical seating portion 13a whose curved surface is shaped to mate with a similarly curved recess in connection 14. By virtue of the curvature of the mating surfaces between seating portion 13a and the connection 14 any misalignment from the required axial direction of the tube can be accommodated so that the tube will not be damaged during insertion through the valve and into the outlet. As shown the tube 13 has four axial gas passageways 13b extending from the top of the tube and emerging in the flat end face 13c of the frusto-hemispherical seating. Although, as indicated above, it is not essential that the hemispherical seating be provided with a flat end face, it may be found advantageous as there is less likelihood of holes 13b being blocked during the formation of the hemispherical portion than if they emerge in the curved region. By way of example only, the tube 13 and the end face 13c may be about 8mm in diameter and the radius of the hemisphere may also be about 8mm in diameter. The axial passageways may each be about 2mm in diameter. The tube may be in excess of 200mm in length, e.g. from 350 to 700mm in length. In Figure 7 is shown a "floating spindle" connection between the lower end of frangible tube 13 and the underside of the valve housing. In this embodiment, the cup-shaped end 13a of frangible tube 13 sits in a complementary recess in the upper face of a floating spindle 20. Spindle 20 is mounted inside annular housing 21 which is clamped via a base 22 to the underside of valve member 8. A sealing O-ring 21a seals housing 21 to base 22. An annular gap 23 is defined between spindle 20 and the interior wall of housing 21. The cup- shaped lower end 13a is attached to the underside of base 22 via a washer 22a. Gas can be introduced into tube 13 via a pipe 24 connected from a source (not shown) into annular gap 23 and passageway 25 in spindle 20 to the base 13a of the tube 13. A plug 26 closes the lower end of housing 21 and is sealed to the inner wall of the housing by an O-ring 27. Plug 26 has an upper annular shoulder 28 whose upper circumference receives a stepped retaining ring 29. The lower part of spindle 20 has a depending central boss 30 and annular shoulders 31. Shoulder 31 rests on the upper surface of retaining ring 29 while boss 30 projects through the retaining ring leaving an annular gap 29a between itself and the ring. Boss 30 has a vertically-extending centrally-disposed cavity which receives the leg of an inverted T-piece connector or keep plate 32. The cross-bar of the inverted "T" rests upon the upper surface 26a of plug 26 between, but spaced from, its shoulders 28. This arrangement permits convenient assembly of the tube 13 and its seating arrangement in housing 21. The annular gaps 23 and 29a allow sideways movement of spindle 20 so that it may "float" and cater for vertical misalignment of the tube 13. This, together with the alignment feature of the cup-shaped end of tube 13, provides a most advantageous arrangement.

Claims: CLAIMS 1. An apparatus to open and close an outlet (5a) in a molten metal handling vessel which includes a valve (6) communicating with the outlet (5a) and having relatively movable valve parts (7, 9 and 8, 11), the valve parts having openings (10, 12) which are displaced from one another to close the valve and, hence, the outlet (5a) and which are in communication with each other and with the outlet to open the outlet, whereby the molten metal can flow out of the vessel, characterised in that there is provided a frangible tube (13) through which gas can be passed, the tube (13) being of sufficient length to extend through both valve parts (7, 9 and 8, 11) and into the outlet (5a) of the vessel, whereby gas can be passed into the outlet and then opening of the valve (6) by relative movement of the valve parts (9, 11) breaks the tube (13) so that it does not obstruct opening and in that the end of the tube (13) has a cup-shaped seating portion (13a) to mate with a similarly- shaped recess in or adjacent the valve (6). 2. An apparatus according to Claim 1, characterised in that the frangible tube (13) extends through a section of the moveable valve part (8, 11) to one side of the valve part's opening (12) and up through the opening (10) in the fixed valve part (7, 9). 3. An apparatus according to Claim 1 or 2, characterised in that the cup-shaped seating portion (13a) of the tube (13) seats in a correspondingly- shaped recess in a connector (14) attached to the underside of the lower valve part (8) of a slide gate valve (6). 4. An apparatus according to Claim 3, characterised in that the connector comprises an annular housing (21) containing a floating spindle (20), the correspondingly-shaped recess being in the upper face of the floating spindle (20). 5. An apparatus according to any preceding claim, characterised in that the cup-shaped seating portion (13a) of the tube (13) is hemispherical or part-hemispherical. 6. An apparatus according to Claim 5, characterised in that the hemispherical, or part hemispherical portion (13a) is of larger diameter than the tube (13) to form a bulbous extension with the pole of the hemisphere furthest from the tube. 7. An apparatus according to Claim 5 or 6, characterised in that the seating portion (13a) is of frusto-hemispherical shape with a flat lower surface. 8. An apparatus according to any preceding claim, characterised in that it includes a gasket surrounding the frangible tube (13) and positioned in the outlet to seal between the relatively movable valve parts (9, 11). 9. A method of opening and closing an outlet (5a) in a molten metal handling vessel in which a valve (6) is positioned to communicate with the outlet, the valve having relatively movable parts (7, 9 and 8, 11), the valve parts having openings (10, 12) which are displaced from one another to close the valve and, hence, the outlet (5a) and which are positioned in communication with each other and with the outlet to open the outlet, whereby molten metal can flow out of the vessel, characterised in that a frangible tube (13) is inserted through the valve parts (7, 9 and 8, 11) into the outlet (5a) while the valve is in the closed position, gas is injected into the outlet (5a) through the tube (13) to remove any obstruction to the outlet and the valve (6) is opened thereby shearing off the length of tube (13) in the outlet (5a) and in that the end of the tube (13) is provided with a cup-shaped seating portion (13a) to mate with a similarly-shaped recess in or adjacent the valve (6). 10. A method according to Claim 9, characterised in that the frangible tube (13) is attached to a connector (14) attached to the underside of the lower valve part (8) of a slide gate valve (6). 11. A method according to Claim 10, characterised in that the connector comprises an annular housing (21) containing a floating spindle (20), the correspondingly shaped recess being in the upper face of the floating spindle, whereby when the tube (13) is inserted through the valve parts (7, 8) the floating spindle may move laterally to allow for vertical misalignment of the tube relative to the outlet. 12. A frangible tube (13) having at least one longitudinal passageway (13b) through which gas can pass, characterised in that one end of the tube (13) has a cup-shaped seating portion (13a) to mate with a correspondingly shaped recess in or adjacent an outlet valve of a molten metal handling vessel. 13. A frangible tube according to Claim 12, characterised in that it is made of ceramic material and has a plurality of longitudinally extending passageways (13b) throughout the length of the ceramic tube. 14. A frangible tube according to Claim 12 or 13, characterised in that a portion of the length of the tube (13) is of ceramic material and the remainder of the length of the tube (13) is of metal. 15. A frangible tube according to Claim 12, 13 or 14, characterised in that the cup- shaped seating portion (13a) is of frusto- hemispherical shape. 16. A frangible tube according to any one of Claims 12 to 15, characterised in that the seating portion (13a) is of larger diameter than the tube (13).

Inventors: BEALE SIMON AUGUSTUS, BEALE, SIMON, AUGUSTUS
Applicants: BEALE SIMON AUGUSTUS, FOSECO INT, BEALE, SIMON, AUGUSTUS, FOSECO INTERNATIONAL LIMITED
Application year: 1994
Main classification: B22D41
IPC codes: B22D41